1. Field of the Invention
The present invention relates generally to high-pressure piston pumps especially adapted for pumping abrasive fluent materials. Particularly, the present invention relates to high-pressure piston pumps for the spray application of highly viscous and abrasive liquid materials.
2. Description of the Prior Art
The spray application of highly viscous liquids and those liquids containing relatively high amounts of abrasive filler material such as industrial coatings has become well known. To provide the high pressure required for these spray applications, various pump designs have been devised. These pump designs incorporate either hydraulic driven piston pumps, hydraulic driven diaphragm pumps or air-operated dual diaphragm pumps.
In hydraulic driven piston pumps, the typical technique utilizes a single piston/cylinder arrangement in which a drive fluid, for example oil, is located on one side of the piston while the abrasive fluid being pumped is located on the other side of the piston. At present, existing pump arrangements of this type can operate at pressures up to 20,000 psi with reasonable reliability. Variations of this design have led to pump designs that incorporate and utilize an output pump and a separate drive pump which are interconnected through a common chamber containing a drive fluid.
U.S. Pat. No. 4,789,313 (1988, Tower et al.) discloses a device that utilizes an output pump and a separate drive pump which are interconnected through a common chamber containing a drive fluid. The output pump includes an output piston within its own pumping chamber for pumping the output liquid by causing the output piston to move through a complete forward stroke. The drive pump includes a drive piston within its own chamber and means for causing the output piston to move the drive piston through its own complete forward stroke. This pressurizes the drive fluid within the common chamber in a way which causes the output piston to move in the forward direction of its stroke. The two pumps are configured such that the forward stroke of the drive piston defines a greater swept volume than the forward stroke of the output piston. This ensures that the output piston will always move through its entire forward stroke before the drive piston.
U.S. Pat. No. 4,598,630 (1986, David T. Kao) discloses a double acting self-flushing pump. The double action slurry pump is provided having a self-flushing piston assembly mounted in a mating cylinder. The piston assembly includes a first piston having a peripheral sealing means and a reciprocating piston rod for driving the first piston. Second and third power pistons mounted adjacent opposite sides of the first piston include sealing discs and form respective first and second chambers with the first piston and the adjacent cylinder wall. The second and third pistons serve to pump the slurry on the sides opposite the flushing fluid chambers. Each of the pumping pistons includes hollow carriers that cooperate with shoulders fixed to the piston rod to provide limited lost motion movement. The resulting lost motion serves to vary the size of the first and second chambers.
U.S. Pat. No. 5,094,596 (1992, Erwin et al.) discloses a pump assembly comprised of a pair of opposed single acting piston pumps operated alternatively by an interposed reciprocal actuator. Each pumping chamber has aligned inlet and outlet check valves in its peripheral wall that defines a straight line path of fluid flow diametrically through the chamber. The piston has its periphery spaced from the peripheral wall of the pumping chamber to provide a relatively short stroke to maintain the straight line path of fluid flow through the chamber. There is an annular seal extending from the peripheral wall toward the piston and bridging the gap between the periphery of the piston and the peripheral wall of the pumping chamber.
U.S. Pat. No. 5,312,028 (1994, James M. Hume) discloses a single stroke pressure viscous liquid pump that includes an upright liquid tank having an open upper end positioned atop a base plate of a frame in coaxial alignment spaced directly beneath a pressure cylinder which includes an axially movable ram having a piston at its lower end. The piston is sized to sealingly engage the inner surface tank whereby downward axial force generated by the ram is transmitted directly against the upper surface of the liquid within the tank. A discharge outlet near the bottom of the tank is connectable to a conduit and liquid spray nozzle. Only a single stroke of the ram is required at a very slow feed rate to empty the tank of liquid thus eliminating virtually all heat buildup.
On one brand of abrasive liquid spraying unit sold by Neal now owned by Ingersold-Rand, there is used a dual piston pump known as the Blaw-Knox SP or Blaw-Knox SSP pump that includes a piston unit having a piston on one end of a piston rod and a second, smaller piston at the other end, each with appropriate piston seals. The piston is within a single unit pump housing having an upper and lower section. The upper section has a smaller diameter than the lower section and houses the small piston. The lower section houses the larger piston which has a check valve situated on the piston rod adjacent the larger piston. The piston rod check valve allows the abrasive liquid to flow from one side of the larger piston to the other. The lower section further includes an abrasive liquid outlet located through the wall of the lower housing portion nearer the junction between the lower and upper housing sections. The abrasive liquid inlet is located on the lower housing end plate. The capability of the Blaw-Knox SP pump and SSP pump is 50 gallons per minute and 100 gallons per minute, respectively.
A disadvantage of the prior art is that the abrasive liquid tends to prematurely wear out the piston seals causing leakage past the upper piston seals, reduced flow through-put of the abrasive liquid, and reduced operating pressure. When the seals fail, the entire piston unit must be removed from the pump housing. This requires removal and disconnection of the hydraulic pump head from the upper section of the housing, of the fluid outlet coupler from the side of the pump housing and of the fluid inlet plate from the lower section pump housing end. The entire piston unit must then be completely removed from the pump housing and the entire pump housing replaced to effect piston seal replacement, even when only the upper piston seals are leaking caused by wear on the seals and on the inside surface of the upper pump housing portion. This type of repair must be done at the company""s shop. This is time consuming and costly because of the downtime for the spray system and because of the replacement of the entire pump housing when the lower pump portion is still functional and not worn.
Even though an abrasive liquid pump is still operable when the seals begin to leak, the pump must be operated at a lower speed to prevent a complete breakdown of the piston seals. This is a particular disadvantage when a sealing spray system is used to seal a large area such as sealing a large asphalt parking lot. This causes the sealing operation to take much longer than anticipated and to subsequently increase the cost of performing the sealing operation. In the event of a seal breakdown that renders the pump inoperable to continue using the sealing spray system, as stated previously, the entire sealing spray system must be transported to the company""s shop to effect a repair.
Therefore, what is needed is an abrasive liquid pump that can be repaired at the job location. What is further needed is an abrasive liquid pump that is less costly to replace the worn seals on the piston unit within the pump housing. What is still further needed is an abrasive liquid pump that does not require replacement of the entire pump housing when the upper seals are worn. What is yet further needed is an abrasive liquid pump that does not have to be completely removed from the sealing spray system to effect a leaking seal repair.
It is an object of the present invention to provide an improved pump housing structure for an abrasive liquid pump that permits the repair of an abrasive liquid pump at the spray-coating job location. It is another object of the present invention to provide an improved pump housing for an abrasive liquid pump that makes it less costly to replace the worn seals on the piston unit and to replace the pump housing. It is a further object of the present invention to provide an improved pump housing for an abrasive liquid pump that does not require the complete removal of the abrasive liquid pump from the sealing spray system to effect a leaking seal repair.
The present invention achieves these and other objectives by providing a two-piece abrasive liquid pump housing that includes an upper pump housing section and a lower pump housing section having a larger inside diameter than the upper pump housing section and that the lower pump housing section is removably attached to the upper housing section. Within the abrasive liquid pump housing, there is a piston rod having a first piston assembly on a first end and a second piston assembly on a second end where the second piston assembly has a larger diameter than the first piston assembly. The piston rod also includes a check valve spaced from the second end adjacent to the second piston assembly. The lower pump housing section also includes an fluid outlet through the wall of the lower pump housing section spaced a predetermined distance from the junction between the lower pump housing section and the upper pump housing section.
The upper pump housing section has a hydraulic pump end and a lower pump housing end. The hydraulic pump end is adapted to be removably connected to a hydraulic pump that provides a hydraulic pump shaft for connection to the piston rod of the abrasive liquid pump. The lower pump housing end is adapted to be removably connected to the lower pump housing section at the end nearest the fluid outlet. A seal is preferably used between the upper pump housing section and the lower pump housing section. The opposite end of the lower pump housing is adapted to be removably connected to a lower housing end cap. The lower housing end cap incorporates a fluid inlet and an inlet check valve.
Because the majority of seal wear occurs at the first piston assembly with associated cylinder wear, the upper pump housing section of the present invention can be easily removed without disconnecting the fluid inlet and outlet connections and without removing the entire abrasive pump from the sealant spray system. Further the piston rod does not have to be removed from the pump housing. The hydraulic power unit is removed from the end of the upper pump housing section and then the upper housing section is removed from the lower pump housing section. By removing just the upper pump housing section, the first piston assembly seals are exposed and can be easily repaired by simply removing the first piston assembly retaining nut(s). New seals are replaced for the old, worn-out seals and the first piston assembly retaining nut(s) are re-connected. A new, replacement, upper pump housing section is re-attached to the lower pump housing section and the hydraulic pump unit is re-attached. The abrasive liquid pump is then ready to operate.